hearth

↻ 2025-11-19

My hearth, heavily used in winter because of wood heating, was unstable due to a floating (separate from main slab) foundation under the concrete block pile which surrounds the stove. The block pile is sinking a little faster than the house, and the hearth is the interface, which cracks tiles very quickly after they are installed, almost seasonally.

The originally specified hearth dimensions were also inadequate for safely containing embers, which would readily roll further than the tile surface from the elevated wood stove.

Let’s try steel plate! It has no grout lines to clean, it’s not flammable, and it won’t crack when the slab shifts.

I used 0.25“ thick AR400 steel plate. This hearth weighs about 383 pounds, so get yourself some lifting magnets and some friends to move it around if you have a similarly large dimensional requirement.

First, we measure out the hearth size (paper tape)

Then demolition

Then leveling concrete so the surface is perfectly flat

Then we plasma cut a piece the correct size and grind off all the mill scale and oil and stuff. This is the hard part. It takes a really long time to grind a piece of steel that large.

Once the steel is complete cleaned up with a grinder, the oxide process (cold gunblue):

• Clean the whole steel surface with alcohol or some power degreaser that leaves no residue. Clean a few times, thoroughly.
• Load a spray bottle which features a fine mist mode with cold bluing solution. I used Birchwood Presto Black BST4.
• Spray the whole surface with the solution from the mist bottle. Spray evenly, everything you want oxided.
• Wait 90 seconds.
• Use a hose to rinse off the oxide solution thoroughly.
• Use a leafblower or compressed air to dry the surface thoroughly.
• Repeat oxide process. I did one coat using the spray bottle, and then did two more coats (waiting 90 seconds, rinsing, and drying between coats) simply dumping and wiping the oxide solution on with paper towel. This gives a cool mottled effect from the spray, a runny effect from the dumping, and an even effect from the wiping.
• When you’re happy with the finish, do a final rinse and dry.
• Coat the steel thoroughly with a protective oil, I use Ballistol or Renaissance Wax. For this hearth, particularly Renaissance Wax, since it’s dries matte.
  

This is what the finish looks like close-up. I love the tool marks from grinding, and I am very happy with the appearance of the oxide.

The plate fit perfectly in the floor.

All done, though the steel does get a little darker over the next few days under the wax finish.

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